This invention relates to improved methods and apparatus for radio frequency (RF) power plasma processing at pressures ranging from about sub-atmospheric pressure to greater than atmospheric pressure.
RF plasma is extensively used in a wide variety of applications for carrying out process operations. The manufacture of semiconductor devices is one area in which plasmas are extensively used. During the manufacture of semiconductor devices, etch processes involving RF plasmas and deposition processes involving RF plasmas are used repeatedly during the fabrication process. One of the main benefits of using plasma and downstream plasma species is the ability of the plasma to stimulate chemical reactions that would otherwise require temperatures that are too high for use in the fabrication of semiconductor devices.
Plasmas are also used in cleaning processes in manufacture of semiconductor devices. The plasmas are commonly used to strip photoresist materials from semiconductor wafers as part of post etch wafer clean procedures. Resist material is stripped from the surface of the wafers by creating a plasma in a gas containing oxidizing species such as oxygen and possibly halogen species that are capable of reacting with and volatilizing the resist material. In some applications, the plasma is maintained at a position upstream of the wafer. Reactive species generated in the plasma flow downstream and react with the wafer surface for the stripping process. Another cleaning process that uses plasmas is the cleaning of reaction chambers used in semiconductor manufacturing.
RF plasmas have also been used for decomposition of chemical compounds that are hazardous or otherwise undesirable. Some of the compounds are highly refractory in nature and are difficult to decompose. Examples of compounds that have been decomposed or abated with plasmas include chlorofluorocarbons (CFC) and perfluorocompounds (PFC).
Clearly, there are numerous applications requiring reliable and efficient methods and apparatus for igniting and sustaining RF plasmas. Unfortunately, typical methods and apparatus for old-style RF plasma systems have characteristics that are undesirable for some applications. There is a need for methods and apparatus for generating RF plasmas that are simple, economical, and capable of operating at atmospheric and sub atmospheric pressures.
This invention seeks to provide methods and apparatus that can overcome deficiencies in known plasma technology. One aspect of the present invention includes methods and apparatus for generating plasmas at pressures ranging from less than one atmosphere to greater than one atmosphere. Another aspect of the present invention includes methods for plasma processing. Still another aspect of the present invention includes apparatus for plasma processing.
One embodiment is a method of generating a plasma; the method being carried out using a microwave power source and a rectangular waveguide, the waveguide having an open end capable of receiving microwaves and a closed end, the open end of the waveguide being connected with the microwave power source so as to be capable of receiving microwave power, the microwave power source being capable of providing microwaves at a wavelength lambda, the waveguide having a gas entry port for flowing a gas into the waveguide, the waveguide having a gas exit port for the gas to exit the waveguide, the gas exit port being located at a distance approximately an odd number of quarter wavelengths lambda from the closed end of the waveguide so that the direction of the electric field lines is substantially parallel to or at an angled to the direction of the exit gas flow, the method comprising the steps of: providing a gas flow through the waveguide so that the gas exits through the gas exit port; providing microwave power to the waveguide so as to create an electric field in the waveguide at the location of the gas exit port; extending an electrically conducting member into the waveguide near the gas exit port so as to facilitate igniting the plasma, wherein the conducting member is connected with an electrical ground, and coupling sufficient microwave power to the gas to sustain the plasma.
It is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. In addition, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out aspects of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention.
The above and still further features and advantages of the present invention will become apparent upon consideration of the following detailed descriptions of specific embodiments thereof, especially when taken in conjunction with the accompanying drawings.